1. Technical Field of the Invention
This disclosure relates generally to a gear pump apparatus, such as a trochoid pump, which is designed to use the meshing of gears to pump fluid by displacement and may be employed with automotive brake systems.
2. Background Art
When a pump body of typical gear pumps is joined using screws to a housing or casing to make a pump unit, tightening of the screws usually results in a variation in axial force acting on parts of the gear pump so as to eliminate air gaps among them. In order to minimize such a variation in axial force, a plate spring is disposed on the top or base of the pump body. The installation of the plate spring, however, requires a space great enough for arranging the plate spring within the gear pump apparatus, thus resulting in a difficulty in minimizing the overall size of the gear pump apparatus.
Japanese Patent First Publication No. 2012-52455 teaches a gear pump designed to have discharge chambers formed outside axial ends of a pump body so as to produce discharge pressure which will press parts of the pump against each other. This eliminates air gaps among the parts of the pump and the need for use of the plate spring which gets in the way of reducing the size of the pump.
The above gear pump includes an outer shell of the housing and ring-shaped sealing mechanisms. The outer shell defines the discharge chambers outside the axial ends of the pump body. The sealing mechanisms are disposed inside the outer shell and pressed against rotors in an axial direction of the rotors, respectively, to hermetically seal the discharge chambers. This structure, however, has the risk of creating an air gap between the outer shell of the housing and each of the sealing mechanisms. Specifically, each of the sealing mechanisms is made up of a plurality of parts. Dimensions of the parts in the axial direction of the rotors are determined in light of the distance between an axial end of a corresponding one of the rotors and the outer shell, but however, variations in dimensions within tolerances of the parts, elastic deformation of the parts resulting from exertion of the discharge pressure, or creep of the parts may lead to the air gaps. The air gaps may result in leakage of pressure or cause elastic parts (e.g., O-rings) of the sealing mechanism to elastically deform thereinto, which will lead to a decrease in durability of the sealing mechanisms.
In order to alleviate the above problems, the axial dimensions of the parts arranged inside the outer shell of the housing may be determined to be great. This, however, causes the rotors to be pressed in the axial direction thereof before the gear pump generates the discharge pressure, thus requiring an increase in torque for driving the rotors, which will result in a loss of pumping torque of the pump.